Miscounts, Duverger's Law and Duverger's Hypothesis

IGIER Working Paper No. 380

37 Pages Posted: 9 Apr 2011

See all articles by Matthias Messner

Matthias Messner

University of Cologne

Mattias Polborn

Vanderbilt University - College of Arts and Science - Department of Economics; CESifo (Center for Economic Studies and Ifo Institute)

Date Written: January 5, 2011

Abstract

In real-life elections, vote-counting is often imperfect. We analyze the consequences of such imperfections in plurality and runoff rule voting games. We call a strategy profile a robust equilibrium if it is an equilibrium if the probability of a miscount is positive but small.

All robust equilibria of plurality voting games satisfy Duverger's Law: In any robust equilibrium, exactly two candidates receive a positive number of votes. Moreover, robustness (only) rules out a victory of the Condorcet loser.

All robust equilibria under runoff rule satisfy Duverger's Hypothesis: First round votes are (almost always) dispersed over more than two alternatives. Robustness has strong implications for equilibrium outcomes under runoff rule: For large parts of the parameter space, the robust equilibrium outcome is unique.

Suggested Citation

Messner, Matthias and Polborn, Mattias K., Miscounts, Duverger's Law and Duverger's Hypothesis (January 5, 2011). IGIER Working Paper No. 380 , Available at SSRN: https://ssrn.com/abstract=1805022 or http://dx.doi.org/10.2139/ssrn.1805022

Matthias Messner (Contact Author)

University of Cologne ( email )

Albertus Magnus Platz
Cologne, NRW 50923
Germany

Mattias K. Polborn

Vanderbilt University - College of Arts and Science - Department of Economics ( email )

Box 1819 Station B
Nashville, TN 37235
United States

CESifo (Center for Economic Studies and Ifo Institute)

Poschinger Str. 5
Munich, DE-81679
Germany

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